U.S. Pat. No. 6,869,474 to Perez-Pena et al., incorporated herein by reference, discusses fast setting of cementitious compositions for producing cement-based products such as cement boards is achieved by adding an alkanolamine to a hydraulic cement such as Portland cement, and forming a slurry with water under conditions that provide an initial slurry temperature of at least 90° F. (36° C.). Additional reactive materials may be included such as high alumina cement, calcium sulfate and a pozzolanic material such as fly ash. The extremely rapid set permits rapid production of cementitious products. Triethanolamine additions have been found to be a very powerful accelerator capable of producing formulations with relatively short final setting times with increased levels of fly ash and gypsum and without the need of calcium aluminate cements. However, formulations with triethanolamine also had relatively lower early-age compressive strength compared to previous cement board formulations containing the calcium aluminate cements.
U.S. Pat. No. 6,641,658 to Dubey, incorporated herein by reference, discusses rapid setting cementitious composition useful for making cement boards containing as reactive powders portland cement, pozzolan, high alumina cement, and insoluble calcium sulfate anhydrite, which provide reduced setting times compared to the prior-art cementitious compositions. The composition preferably comprises as a reactive powder blend 35 to 90 wt. % Portland cement, 0 to 55 wt. % pozzolan, 5 to 15 wt. % high alumina cement, and 1 to 8 wt. % insoluble calcium sulfate anhydrite. Substitution of insoluble calcium sulfate anhydrite for conventional soluble gypsum (a dihydrate) increases the release of heat and decreases setting times, despite the use of very high amounts of pozzolanic materials, preferably fly ash. The cementitious composition may also include lightweight aggregates and fillers, plus additives to impart other useful properties as desired, such as superplasticizers, set retarders, and set accelerators.
U.S. Pat. No. 4,488,909 to Galer et al., incorporated herein by reference, discusses cementitious compositions capable of rapid setting. The compositions permit high speed production of carbon dioxide resistant cement boards by forming essentially all of the potential ettringite within about 20 minutes after the composition is mixed with water. The essential components of the cementitious composition are Portland cement, high alumina cement, calcium sulfate and lime. Pozzolans such as fly ash, montmorillonite clay, diatomaceous earth and pumicite may be added up to about 25%. The cement composition includes about 14 to 21 wt. % high alumina cement, which in combination with the other components makes possible the early formation of ettringite and other calcium aluminate hydrates responsible for early setting of the cementitious mixture. In their invention, Galer et al. provided aluminates using high alumina cement (HAC) and sulfate ions using gypsum to form ettringite and achieve rapid setting of their cementitious mixture.
Ettringite is a compound of calcium aluminum sulfate compound having the formula Ca6Al2(SO4)3.32H2O or alternatively 3 CaO.Al2O3.3CaSO4.32H2O. Ettringite forms as long needle-like crystals and provides rapid early strength to cement boards, so they can be handled soon after being poured into a mold or over a continuous casting and forming belt.